Over the years, computer applications have moved from highly centralized mainframes to the desktop. More recently, computing power has moved to mobile devices, such as cellular telephones, personal digital assistants, and sensors embedded unobtrusively in the environment and objects placed in the environment.
One example of this application uses radio-frequency identification (RFID) tags, see Want, “RFID, A Key to Automating Everything,” Scientific American, vol. 290(1), 56–65, 2003. RFID tags can be as small as a grain of rice, are cheap, e.g., a fraction of a dollar, and can transmit a unique identity to a tag-reader over a range in meters.
Conventional radio-frequency identification (RFID) tags are used to identify objects, including animals and people. RFID tags provide an alternative to bar codes for distinguishing and recording products for purchase. RFID tags can result in labor savings to manufacturers, distributors, and retailers. Annual estimated saving for a larger retailer using RFID tags could amount to billions of dollars per year.
The typical prior art RFID system includes a microchip and an antenna. The antenna can be in the form of a tuned induction coil. The operation is fundamentally simple. Typically, the microchip stores a unique identification code that can be detected when the antenna of the tag couples inductively with an antenna of the reader. This coupling changes the impedance, hence the load at the receiving antenna. The load can be modulated according to the stored identification code, by switching the coil in and out.
Conventional RFID tags can be characterized according to the following basic attributes. An active RFID tag includes a power source to operate the microchip and to ‘broadcast’ the signal to the reader. Semi-passive tags use a battery to operate the microchip, but use an induced current to operate the transmitter. Because these types of tags are more costly to manufacture, they are typically used for high-cost objects that need to be identified at greater distances. For passive tags, the reader induces a current in the tag by emitting electromagnetic radiation. These tags are relatively cheap, and are effective up to ranges of about 50 meters, depending on the power of the transmitted RF signal.
The tag can be read only, or read and write. In the later type, information can be added to the tag over time using a memory. For example, the tag can store when it was read, or how often it was read.
Existing commercial applications include non-contact access control, ear tags for livestock, and consumer products. More sophisticated tags go beyond simply transmitting an identity. Modern tags embed significant computation power and data. This presents the problem of retrieving and identifying the data provided by RFID tags.
A number of applications are known where real-world objects and environments are augmented with data and small processors.
A number of techniques are known for adding ‘intelligence’ to objects and, in some cases, building human interactions around intelligent objects. The SenseTable system tracks and augments the area around sensing tablets on a tabletop using a projector, Patten et al., “SenseTable: A Wireless Object Tracking Platform for Tangible User Interfaces,” Conference on Human Factors in Computing Systems, ACM CHI, 2001. Intelligent furniture is described by Omojola et al., “An installation of interactive furniture,” IBM Systems Journal, Vol. 39(3,4), 2000.
Some systems use active RF tags that respond to laser pointers. The FindIT flashlight uses a one-way interaction and an indicator light on the tag to signal that a desired object has been found, see Ma et al., “The FindIT Flashlight: Responsive Tagging Based on Optically Triggered Microprocessor Wakeup, Ubicomp, pp. 160–167, 2002.
Other systems use a two-way interaction, where the tag responds back to a PDA using a high-power complex communications protocol, such as IEEE 802.11 or X10, Patel et al., “A 2-Way Laser-Assisted Selection Scheme for Hand-helds in a Physical Environment,” Ubicomp, 2003, and Ringwald, “Spontaneous Interaction with Everyday Devices Using a PDA, UbiComp, 2002.
Interaction and Augmentation
Interaction with laser pointers for large display screens is common. A number of sensing and interaction techniques for mobile devices are described by Hinckley et al., “Sensing Techniques for Mobile Interaction,” ACM UIST CHI Letters, Vol. 2(2), pp. 91–100, 2000.
Augmentation of physical world objects has been primarily achieved via eye-worn or head-mounted displays, see Azuma et al., “Recent Advances in Augmented Reality, IEEE Computer Graphics and Applications, vol. 21(6), pp. 34–47, 2001, or hand-held screens. Screen-based augmentation using PDA, camera and RFID tags is described by Want et al., “Bridging Physical and Virtual Worlds with Electronic Tags,” ACM SIGCHI, pp. 370–377, 1999, and Rekimoto et al., “Augmentable Reality: Situated Communication through Digital and Physical Spaces,” IEEE 2nd International Symposium on Wearable Computers (ISWC 98), pp. 68–75, 1998.
Projector-based augmentation has been described by Underkoffler et al., “Emancipated pixels: Real-world graphics in the luminous room,” Proc. Siggraph 99, ACM Press, pp. 385–392, Pinhanez, “The Everywhere Displays Projector: A Device to Create Ubiquitous Graphical Interfaces,” Ubiquitous Computing, 2001, Raskar et al., “Shader lamps: Animating real objects with image-based illumination,” Rendering Techniques 2001, Proceedings of the Eurographics Workshop, 2001, Bimber et al., “The virtual showcase,” IEEE Comput. Graph. Appl. 21, 6, pp. 48–55, 2001, and Verlinden et al., “Development of a Flexible Augmented Prototyping System,” The 11th International Conference in Central Europe on Computer Graphics, Visualization and Computer Vision '2003, 2003.
Image warping for a hand-held projector to support shape and object adaptive projection is described by Raskar et al., “ilamps: geometrically aware and selfconfiguring projectors,” ACM Trans. Graph. 22, 3, pp. 809–818, 2003.
Adding distinctive visual markers for tracking is not always practical. Therefore, it is desired to augment environments and objects without adding infrastructure to obtain a 3D context.
Location sensing systems such as the Olivetti Active Badge, see Want et al., “The active badge location system,” ACM Trans. Inf. Syst. 10, 1, pp. 91–102, 1992, and Xerox PARCtab, Want et al., “An Overview of the ParcTab Ubiquitous Computing Experiment, IEEE Personal Communications, pp. 28–43, 1995, recover location, but have typically been used for passive tracking, and not for interactive systems.
Laser-pointer systems for interacting require a user to identify a target object and direct the pointer at the object to initiate interaction. But accurate pointing is difficult when the tags become visually imperceptible, and multiple tags can only be dealt with serially.
It is desired to provide a system and method that can locate and identify tags placed on objects and in the environment.